The present invention relates to an apparatus and method for controlling an industrial robot.
In the operation of an industrial robot with several degrees of freedom, it is found increasingly necessary to go, as far as the hand/operating point of its arm is concerned, from a position control to a position regulation, i.e., to feed back sensor data via the hand/operating point, closing the control loop, and not only to set, for instance, axis angles of the industrial robot to preset values. For one, a position control requires expensive mechanical drive designs if high repetition accuracy for programmed motions of the robot arm is to be achieved; secondly, process-dependent track corrections should be possible.
A system according to the generic term for controlling an industrial robot is known, for instance, from DE-OS No. 32 44 307 or from the journal Industrie-Anzeiger 106 (1984) 23, page 31 and is reproduced schematically in FIG. 2 of the present description.
Track points (for instance, Cartesian location vectors x) sequentially predetermined by an interpolation unit IPO in (Cartesian, global) coordinates independent of the robot are transformed at the clock rate of the interpolation IPO (interpolation clock frequency=f.sub.I) by a transformation unit T1 into robot-referred coordinates (for instance, axis angles) and fed to a position control L. The clock frequency f.sub.L thereof is several times the interpolation clock frequency f.sub.I in order to provide, within an interpolation cycle, graduated reference settings to the drives of the industrial robot IR and to cause motions of the arm members controlled (for instance, also with respect to velocity and acceleration) of the industrial robot IR. A sensor S picks up the actual or relative position of the hand/operating point HP/AP (position, for instance, relative to a work piece, a welded seam, etc.), and a sensor data processing unit V generates from the sensor signal s a correction vector c which is defined in the robot-independent coordinate system and is fed back, closing the control loop.
In this connection it should be noted that the feedback branch is conducted to a summing point .epsilon. at the input of the transformation unit T1 in order to transform the correction vector c implicitly into the robot-referred coordinate system with the respectively next track point x given by the interpolation unit IPO. This type of feedback, however, has the disadvantage inherent in the system, that the hand/operating point control takes into account a change of the sensor signal possibly only after a full interpolation cycle.